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Chapter 10: Q11CQ (page 466)
Explain the dependence of conductivity on temperature for conductors and for semiconductors.
The conduction band of the semiconductor will be partially filled with electrons as the temperature rises, and so the resistance of the semiconductor will decrease.
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Electron affinity is a property specifying the "appetite" of an element for gaining electrons. Elements, such as fluorine and oxygen that lack only one or two electrons to complete shells can achieve a lower energy state by absorbing an external electron. For instance, in uniting an electron with a neutral chlorine atom, completing its n = 3 shell and forming a CI ion, 3.61 eV of energy is liberated. Suppose an electron is detached from a sodium atom, whose ionization energy is 5.14 eV.Then transferred to a (faraway) chlorine atom.
(a) Must energy on balance be put in by an external agent, or is some energy actually liberated? If so How much?
(b) The transfer leaves the sodium with a positive charge and the chlorine with a negative. Energy can now be extracted by allowing these ions to draw close forming a molecule. How close must they approach to recover the energy expended in part (a)?
(c)The actual separation of the atoms in a NaCl molecule is 0.24 nm. How much lower in energy is the molecule than the separated neutral atoms?
It is often said that the transistor is a basic element of amplification, yet it supplies no energy of its own. Exactly what is its role in amplification?
Question: - Verify using equation (10-12) that the effective mass of a free particle is m.
Question: In a diode laser electrons dropping from the conduction band across the gap, and into the valence band produce the photons that add to the coherent light. The ZnTe laser has a band gap of 2.25 eV. About what wavelength laser light would you expect it to produce?
The accompanying diagrams represent the three lowest energy wave functions for three "atoms." As in all truly molecular states we consider, these states are shared among the atoms. At such large atomic separation, however, the energies are practically equal, so anelectron would be just as happy occupying any combination.
(a) Identify algebraic combinations of the states (for instance, 5+11/2+11/2 ) that would place the electron in each of the three atoms.
(b) Were the atoms closer together, the energies of states 1.11, and III would spread out and an electron would occupy the lowest energy one. Rank them in order of increasing energy as the atoms draw closer together. Explain your reasoning.
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